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About Robert Jemison Van De Graaff

Robert Jemison Van de Graaff (December 20, 1901 – January 16, 1967), was an American physicist, noted for his design and construction of high voltage generators, who taught at Princeton University and MIT.

Biography

Robert Jemison Van de Graaff was born at the Jemison-Van de Graaff Mansion in Tuscaloosa, Alabama, from Dutch descent. In Tuscaloosa, he received his BS and Masters degrees from The University of Alabama where he was a member of The Castle Club (later became Mu Chapter of Theta Tau). After a year at the Alabama Power Company, Van de Graaff studied at the Sorbonne. In 1926 he earned a second BS at Oxford University on a Rhodes Scholarship, completing his PhD in 1928.

Van de Graaff was the designer of the Van de Graaff generator, a device which produces high voltages. In 1929, Van de Graaff developed his first generator (producing 80,000 volts) with help from Nicholas Burke at Princeton University. By 1931, he had constructed a larger generator, generating 7 million volts. He was a National Research Fellow, and from 1931 to 1934 a research associate at the Massachusetts Institute of Technology. He became an associate professor in 1934 (staying there until 1960). He was awarded the Elliott Cresson Medal in 1936.

During WWII, Van de Graaff was director of the High Voltage Radiographic Project. After WWII, he co-founded the High Voltage Engineering Corporation (HVEC). During the 1950s, he invented the insulating-core transformer (producing high-voltage direct current). He also developed tandem generator technology. The American Physical Society awarded him the T. Bonner prize (1965) for the development of electrostatic accelerators.

The Van de Graaff generator uses a motorized insulating belt (usually made of rubber) to conduct electrical charges from a high voltage source on one end of the belt to the inside of a metal sphere on the other end. Since electrical charge resides on the outside of the sphere, it builds up to produce an electrical potential much higher than that of the primary high voltage source. Practical limitations restrict the potential produced by large Van de Graaff generators to about 7 million volts. Van de Graaff generators are used primarily as DC power supplies for linear atomic particle accelerators in nuclear physics experiments. Tandem Van de Graaff generators are essentially two generators in series, and can produce about 15 million volts.

The Van de Graaff generator is a simple mechanical device. Small Van de Graaff generators are built by hobbyists and scientific apparatus companies and are used to demonstrate the effects of high DC potentials. Even small hobby machines produce impressive sparks several centimeters long. The largest air insulated Van de Graaff generator in the world, built by Van de Graaff himself, is operational and is on display at the Boston Museum of Science. Demonstrations throughout the day are a popular attraction. More modern Van de Graaff generators are insulated by pressurized dielectric gas, usually freon or sulfur hexafluoride. In recent years, Van de Graaff generators have been slowly replaced by solid-state DC power supplies without moving parts. The energies produced by Van de Graaff atomic particle accelerators are limited to about 30 MeV, even with tandem generators accelerating doubly charged (for example alpha) particles. More modern particle accelerators using different technology produce much higher energies, thus Van de Graaff particle accelerators have become largely obsolete. They are still used to some extent for graduate student research at colleges and universities and as ion sources for high energy bursts.